302 INNERVATION. [CHAP.XI. 



fibres which take an upward course pass into the gray matter, or 

 simply merge into the longitudinal fibres of the cord and pass 

 upwards to the brain. Mr. Grainger' s researches lead him to sup- 

 pose that each root consists of a double set of fibres one which 

 penetrates, and has its origin from, the gray matter, and the other 

 which is continuous with the longitudinal fibres. This view is con- 

 sidered to derive probability from the hypothesis which ascribes the 

 voluntary and involuntary actions of the cord to two distinct series 

 of fibres, of which one is under cerebral influence, and the other 

 merely excito-motory ; and it might be acknowledged to do so, if 

 the necessity of distinct fibres for the two kinds of action were first 

 proved. It is possible, however, that all the fibres penetrate and 

 arise from the gray matter. But we have seen nothing to justify 

 Stilling and Wallaces assertion, that the anterior and posterior 

 roots coalesce in the gray matter, forming loops, the convexities of 

 which are directed to the centre of the cord ; and we have already 

 stated our reasons (p. 2'59) for doubting the fibrous nature of the 

 lines which these writers represent as radiating between the gray 

 matter and the surface of the cord. 



The posterior roots adhere to the posterior part of the antero- 

 lateral column, and are doubtless closely connected with the poste- 

 rior horns of gray matter. In separating the columns of the cord 

 along the line of sequence of the fascicles of the posterior roots, we 

 have always found these roots to remain with the antero-lateral 

 columns, and to have little or no connexion with the posterior 

 ones. We would therefore refer the origin of these nerves to the 

 posterior horns of gray matter, and to the posterior part of the 

 antero-lateral columns. 



Of the Encephalic Nerves. The arrangement of these nerves, 

 originally proposed by Willis, although open to many objections, 

 has nevertheless been so long adopted in this country and on the 

 Continent, and is so constantly used by scientific as well as prac- 

 tical writers, that to abandon it would be productive of great 

 inconvenience, and would be of no advantage, unless some other 

 arrangement of unexceptionable kind could be substituted for it. 

 In the absence of any such new mode of arrangement, we propose 

 to adhere to that of Willis; at the same time remarking, that 

 much of the imperfection of it is obviated by naming each pair 

 of nerves from some prominent feature either of its function or its 

 anatomical connexions. 



Twelve pairs of nerves are found connected with the base of the 

 encephalon. Five pairs have been so classed by Willis as to form 



